The present invention relates generally to rotary machines, and, more specifically, to a rotary compressor, pump, or engine.
In one type of rotary machine, a rotor is mounted for rotation inside an oblong stator casing. The rotor includes a plurality of circumferentially spaced apart perimeter slots from which extend radially outwardly a respective plurality of vanes. Each of the vanes has a radially outer tip which slides along the casing as the rotor rotates during operation, with the oblong casing causing the vane to reciprocate radially in and out of the rotor slots as the rotor rotates.
The oblong casing defines with the perimeter of the rotor two generally crescent working chambers through which the reciprocating vanes travel. In one chamber, a working fluid such as air is compressed by the rotating vanes. Both working chambers may be similarly configured for air compression and therefore may define a rotary compressor. Or, fuel may be injected into the compressed air and suitably ignited for undergoing expansion in the second chamber for defining an internal combustion rotary engine. In both examples, the vanes either impart energy into the fluid being compressed, or extract energy from the expanding combustion gases, with associated forces being carried through the rotor and cooperating drive shaft.
Rotation of the rotor during operation generates significant centrifugal force on the individual vanes which is reacted by the cooperating casing. The vane tips must therefore be suitably lubricated for decreasing undesirable frictional wear between the vane tips and the casing. In order to reduce the centrifugal forces on the vane tips, the vanes are preferably made as light as possible, yet must also be sufficiently strong for accommodating the reaction forces of compressing the fluid or expanding the gas with a suitable useful life.
An exemplary rotary engine is disclosed in U.S. Pat. No. 5,571,244-Andres which includes lightweight ceramic vanes having an air bearing and seal at the vane tips. Pressurized air is channeled through the vanes and tips from which it is discharged to form a thin air blanket between the vane tips and the cooperating casing. The air blanket provides a low friction air bearing for reacting the centrifugal forces generated in the vanes, and also provides an effective fluid seal for separating the working fluid on both sides of the vane.
The oblong casing disclosed in this patent includes two semi-circular arcuate portions and two flat portions disposed therebetween. The traveling vane tips must therefore transition between the arcuate and flat portions of the casing. At the center of the flat portion and along the arcuate portions of the casing, the vanes travel perpendicular thereto. However, on both off-center sides of the flat portions, the vanes are necessarily non-perpendicular thereto at relatively small tilt angles. The non-perpendicular alignment of the vanes relative to the off-center portions of the flat casing increases the difficulty of establishing an effective air bearing and seal between the vane tips and the casing.
The Andres patent identified above discloses two tip arrangements for providing effective vane tip seals and bearings. However, these arrangements are geometrically fixed in relationship to the vanes, and necessarily change angular orientation relative to the casing at the off-center flat portions thereof. The bearing gap between the vane tips and the casing therefore becomes nonuniform at the off-center flat portions which decreases the effectiveness of the air bearing and seal at the vane tips.
Accordingly, it is desired to provide an improved vane for a rotary machine having a self-aligning, lubricated vane tip.